There was really only one moment worth watching at last month's Oscars. At the end of a dull ceremony, a chorus of 10-year-olds took to the stage and sang Over the Rainbow with joyful lack of inhibition and more feeling than most Oscar-winning performances. But that would have been no surprise to the 10 million people who have watched PS22's pop covers online. PS22 is the largest elementary school on New York's Staten Island, an unremarkable, state-funded school with a thoroughly remarkable fifth-grade chorus. Tori Amos, Kylie Minogue and Beyoncé are among their fans; after they covered Just Dance, Lady Gaga called them: "Fabulous. Perfect. Soulful. Amazing." Now, as 10-year-old Azaria says: "We've met so many celebrities we've forgotten half of them!" They've also covered more esoteric fare, like Ariel Pink's Round and Round.

The week after the Oscars, the sign outside the school reads: "We welcome home Hollywood's newest stars, PS22 Chorus!" As I'm signing in at reception, a door bursts open and there's chorus director Gregg Breinberg flinging open his arms to hug me. There's a lot of hugging over the next few hours. As Breinberg walks around the school, kids mob him, yelling: "Hi, Mr B!" The school has 1,200 pupils, but he seems to know everybody's name.

When he started the chorus 10 years ago, he was newly arrived in the school and worried about the security of his position. "I was trying to be the music teacher that I thought I was supposed to be and not the music teacher that I am," he explains, over a hasty pizza lunch. Eventually, he threw caution to the wind and decided to follow his instincts. "I always tell the kids that the most interesting music can come when you break the rules. That holds true for our chorus. They have a unique sound: these kids do not sound like typical elementary school kids."

Almost more moving than the sound they make is how expressive they are as performers. They sway and groove and make idiosyncratic hand movements along to the lyrics, finishing each song with whoops and yells. How does he get that sort of uninhibited performance from them?

"Because if you don't stop 'em, they do it naturally," he says, grinning. "It's what happens when you put them in a setting where they're comfortable and where it's OK to goof. In the context of the group, that team spirit means they can really rise above their limitations."

And there are plenty of those. Most of the kids come from economically disadvantaged families and, as Breinberg says, many "really had big issues with behaviour. A lot are in special education." Pupils only get to be in the chorus if they work hard and behave well. At the start of each academic year, Breinberg holds auditions and casts a new chorus, "and kids that really couldn't sing on the pitch at the beginning but loved it and wanted it so bad that I just had to give it to them, they end up actually on key by the end of the year". Today, former member 18-year-old David Bobe has come back to tell the chorus he's just been invited on to American Idol.

Nonetheless, "these are not prodigies," Breinberg says. "It's that group dynamic that makes this amazing thing happen. Hopefully I inspire them just the same way they inspire me. I think that's why it works – there's this whole foundation of respect: respect for me; respect for them; respect for the music."

And then it's time for practice. Half-eaten pizza slice in hand, he yells "Chorus!" through the corridors and kids come running. They're working on a version of the national anthem for an ice hockey game at Madison Square Garden the following week.

The words are written on a whiteboard and he goes through each line patiently. "Does anybody know what ramparts are?" he asks. "Craziness?" offers one pupil. "Parts of a ramp?" suggests another.

It's a reminder that though they may sing with more soul than most of the artists they cover, they are still, of course, just kids. Cheering each other on, they all say that the best thing about being in chorus, as 10-year-old Jonathan puts it, is that "it makes everyone feel like they have more friends".

"The best feeling," says Breinberg, "is when you see those kids rising above themselves. We just want to give them something to hold on to and something to inspire them to be better people. And all the beautiful music is almost incidental, you know?"